Since agglomeration was first introduced, there have been many attempts to produce an agglomerated coffee product which has a roast and ground appearance. Such an appearance would have a beneficial impact on the consumer who equates the appearance of roast and ground coffee with the taste and quality of freshly brewed coffee. The product must, however, satisfy other criteria to be acceptable to the consumer. For example the product must have sufficient bulk density to produce about one cup of coffee per teaspoon of product. If the product is too dense, then too strong a cup of coffee will result and if the product is not dense enough the coffee will be too weak. The product must also possess sufficient structural strength so as not to produce a large number of fines and the product must have a dark pleasing look and suitably will have a vari-colored appearance. Furthermore, the product must be rapidly soluble without producing foam and the product should be of about the same size distribution of roasted and ground coffee. In addition, for the product to be commercially feasible, the product must be capable of being prepared at commercially acceptable rates.
An effort directed to agglomerating instant coffee is U.S. Pat. No. 2.977,203 issued to Sienkiewicz et al. entitled "Agglomerating Process" which is typical of the early teachings in the soluble coffee agglomeration field. The patent describes an agglomerating procedure whereby a plane of discretely arranged powder particles which are moving in a first direction preferably in the form of a falling curtain are contacted by a jet of steam, thereby redirecting the particles. As the particles in the curtain enter the path of the jet of steam, they immediately become wetted. By being directed in the path of the jet of steam, they are caused to contact one another. The opportunity for contact or collision results in a greater percentage of agglomeration. The turbulence created by the jet of steam allows a maximal opportunity for collision or contact of the wetted particles. U.S. Pat. No. 3,554,760 to Sienkiewicz et al. is an improvement of the above-described patent involving the use of upper and lower jets of steam which impinge against the falling curtain of powder. The upper jets of steam form agglomerates of varying size, density, and moisture content; the lower jets act to further wet the agglomerates and render them more uniform in density, size, and moisture content. This process, however, produces an irregular, jumbled agglomerate mass which does not have the surface appearance of roasted and ground coffee.
On the other hand, U.S. Pat. No. 3,716,373 issued to Rhodes et al. teaches a process for producing an instant coffee composition in the form of a free-flowing soluble agglomerated powder which comprises milling soluble coffee particles and forming clusters therefrom by feeding the milled particles into a vibrating distributor box. A sufficient depth of milled particles are maintained in the box, such that the particles are substantially compacted and form the desired clusters on release from the box. The resulting clusters are fed into a zone where they are moistened and heated thereby forming an agglomerated granular powder which is then dried; agglomerated powders having a bulk density of from 0.25 to 0.40 grams per cc and a color of from 28 to 40 Lumetron Units are then produced. Thus, this product is dense and relatively light in color.
British Pat. No. 1,276,437 in the name of Rhodes and Clark teaches an improvement in this above-identified process; the agglomerate produced by this improved process can have a lower bulk density range if the feed material, likekwise, has a lower density than the normal spray-dried coffee powder which was used in the process described in U.S. Pat. No. 3,716,373. The British patent to Rhodes et al. talks of drying a foamy product to produce a feed material which has a bulk density before milling of 0.05 to 0.18 grams per cc at a residual moisture content of from 2 to 7% by weight; the agglomerate is said to have a bulk density of from 0.22 to 0.34 grams per cc, a color of from 28 to 50 Lumetron Units and a hardness less then 10. This product is thus light in color.
Still another process is that set forth in the British Pat. No. 2,006,603 issued to Morgan et al. teaching a coffee product consisting of free-flowing agglomerates which comprise soluble coffee particles and finely ground roasted coffee, the finely ground roasted coffee being present in an amount of from 2 to 20% by weight. A product with a roasted and ground appearance is not described.
While the coffee art is thus replete with numerous examples of ways to agglomerate coffee products, there is still a need for a process of producing an agglomerated instant cofee which will result in a product possessing a truly roast and ground coffee appearance while at the same time having an acceptable density, be sufficiently strong, have suitable dark color appearance, and be produceable at commercially acceptable rates.